1. Field of the Invention
The present invention relates generally to drilling equipment, and in particular, to sub-surface drilling equipment which utilizes a pneumatic drilling chip removal system.
2. Background Information
In the drilling or making of a hole into any substrate for the primary purpose of producing a gas or liquid, as the hole for the well is bored out, it is an operational requirement to remove the drilling debris cut and chipped away, hereinafter referred to as drilling chips, from the bottom of a well bore.
Frequently in well drilling operations, these drilling chips are removed from the well bore with the use of drilling mud. Drilling mud is a liquid/chemical composition that is injected down the central passageway of the sub-surface drilling equipment and is ejected out through apertures in the drilling bit at the bottom of the well bore. The drilling mud picks up the drilling chips as the drill bit chips them from the substrate and moves upward in the annulus (the space between the well sidewall and the sub-surface drilling equipment). Both drilling mud and the drilling chips contained therein are discharged at the surface into a means for separating the drilling chips and other solid material from the drilling mud.
Drilling mud has a number of disadvantages. Water base drilling mud is expensive to mix and maintain; oil base and polymer base drilling mud are usually leased, and like water base, both are very expensive to maintain. These drilling muds must be handled carefully due to their toxicity, and must be recycled during drilling operations. That is, recycling equipment must be used to remove drilling chips from the drilling mud, so that the drilling mud may be reused again. The drilling mud, due to its toxicity, also requires special disposal methods. Finally, drilling time is increased when drilling mud must be used. In average rock or rock-like substrate, the drilling time when drilling mud is utilized is about three to fifteen minutes per foot. Drilling mud is required, however, at a certain depth, in most drilling operations. The reasons behind this requirement will be explained below.
In the instance of a relatively hard substrate, it has been recognized that drilling chips are generally light enough to be removed from a well bore through the use of a pneumatic drilling chip removal system, which utilizes high pressure air rather than drilling mud for the removal of drilling chips from a well bore. In effect, as the well bore is deepened, and the sub-surface drilling equipment is progressively lowered into the well bore, a controlled volume of high pressure air is injected into the central passageway of the sub-surface drilling equipment. The air is ejected out through jets in the drilling bit at the bottom of the well bore. As the drilling chips are chipped from the substrate by the drilling bit, the drilling chips are picked up and propelled upward by the air ejected from the drilling bit at the bottom of the well. The air forms an air stream up the annulus of the well which carries the drilling chips up the annulus to the surface where the drilling chips are removed. Pneumatic drilling chip removal is desirable in hard substrate, because the well may be drilled more rapidly with a pneumatic drilling chip disposal system. On the average, a pneumatic drilling chip removal system permits the well bore to be deepened at the rate of about one to three feet per minute. Since no costly drilling materials, such as drilling mud, recycling equipment, or specialized disposal is required, the cost of drilling using a pneumatic drilling chip removal system are much less than conventional drilling operations using drilling mud to remove drilling chips. Further, since toxic material is not involved, the use of pneumatic drilling chip removal is generally safer than the continued use of drilling mud for the entire well.
In the normal operation of sub-surface drilling equipment, a drilling bit is connected to a plurality of drill collars. The drilling bit is of the type normally used in a substrate which is comprised basically of a solid or rock-like formation. The drill collars disposed immediately above the drilling bit are connected end to end, each drill collar having a central passageway. The plurality of drill collars are coupled together in segments. Each segment comprises one or more drill collars of the same external diameter. Each segment has a smaller outer diameter as compared to the next lower segment of drill collars. The respective segments of drill collars are connected together by a change over sub, which connects each segment together. That is, when a larger size drill collar is to be attached to a similar drill collar of a smaller size, a change over sub is normally utilized. The change over subs act as adapters between segments, and also have a central passageway disposed therethrough. The segments of drill collars with their respective change over subs are termed the bottom hole assembly. Immediately above the interconnected segments of drill collars is the drilling string, which comprises a plurality of drill pipe connected end to end. The drilling string also has a central passageway which extends therethrough and connects to the central passageway of the drill collars segments. A change over sub (or, a top collar sub) is utilized to connect the lowest drill pipe in the drilling string to the highest drill collar of the bottom hole assembly.
The central passageway creates a passage for pressurized air which is injected at the surface via a pressurized air source. The pressurized air passes through the entire length of the sub-surface drilling equipment via the central passageway to the drilling bit at the bottom of the well. The air from the central passageway is ejected from the drilling bit via air jets in the drilling bit and travels upward through the annulus for expulsion at the surface. As the pressurized air travels upward from the bottom of the well bore to the surface, the air carries the drilling chips to the surface for removal.
In normal drilling operations, the segment having the largest drill collars are connected immediately above the bit, with size and external diameter of each consecutively higher segment of drill collars decreasing. The drilling string comprises the longest segment of the sub-surface drilling equipment, and also the segment having the narrowest external diameter. The drilling string connects to the surface drilling equipment, and to a source of pressurized air, so that air may be directed down the sub-surface equipment, as previously described. The sub-surface equipment can be formed of sufficient length to extend from the surface to a subterranean liquid or gas bearing reservoir. The pneumatic drilling chip removal system, however, may be utilized, generally, for only about 1,000-3,000 feet when drilling large diameter holes.
Due at least in part to the conical neck of the change over subs, and the narrowing of the sub-surface drilling equipment in the upper portions of the annulus, thereby increasing the annular space significantly in the well bore, the present pneumatic drilling chip removal system has been inadequate for removal of drilling chips at depths generally greater than 3,000 feet in large diameter holes. This is due to significant suspension of drilling chips in the annulus as the depth of the well bore increases, as well as significant drilling chip accumulation in the bottom of the well bore.
The conical neck of the change over subs, the progressive narrowing of the sub-surface equipment as it approaches the surface, and the depth of the well bore create air spaces having an ineffective air lift in which the drilling chips increasingly become suspended or become deposited, creating blockages. These ineffective air spaces are referred to herein as "critical lift areas." In addition, when the pressurized air is turned off, and additional drill pipe is added to the sub-surface equipment, the drilling equipment must be raised by the draw works, and the drilling chips suspended in the annulus or deposited against the conical surfaces of the change over subs fall to the bottom of the well bore. The drilling bit must then re-drill through these drilling chips, and the re-drilling process consumes significant time. That is, on an average, re-drilling through drilling chips in the bottom of the well bore frequently is much more time consuming than drilling the rock or rock-like substrate. Eventually, the blockage of drilling chips, and re-drilling the well bore through the drilling chips, reduces drilling efficiency such that another means of drilling chip removal, namely, drilling mud, must be utilized.
In overcoming this operational problem, which is currently encountered in present pneumatic systems for removing drilling chips from a well bore, disclosed herein is a means whereby portions of the sub-surface drilling equipment is adapted to furnish a supplementary flow of air directly into the annulus at critical lift areas. "Critical lift areas" are defined as areas where there is inadequate air velocity to propel drilling chips upward in the annulus, so that such drilling chips may be removed at the surface. These supplementary pressurized air flows are introduced at points where they will add and maintain the velocity of the air flow in the critical lift areas and throughout the annulus as the external diameter of the upper drill collars decrease, thereby reducing and/or eliminating critical lift areas and the associated suspension and/or accumulation of drilling chips in significant amounts. In the present invention, as the area in the annulus between the sub-surface drilling equipment and the well bore increases, so does the air flow. This additional air flow in the critical lift areas maintains the overall velocity of the air flow within the annulus, and the drilling chips therefore continue to be propelled to the surface, therefore reducing and/or eliminating drilling chip build up and drilling chip blockages in the annulus.
The supplementary air is furnished by tapping the primary air flow from the central passageway. The change over subs and/or the drill pipe, as well as other drilling equipment, are adapted as will be described in detail below, to selectively direct air flow into the critical lift areas via conduits containing specialized valves. The selectively directed air flow is triggered by increased air pressure in the central passageway and the annulus, that is, when significant drilling chip accumulation in the annulus has begun, or, alternatively, when the depth of the well requires increased air velocity to propel the drilling chips through the annulus to the surface.
An advantage of the pneumatic drilling chip removal system described herein is to permit much more extensive use of pneumatic drilling chip removal while drilling both large diameter well bores as well as small diameter well bores. Further, it will be appreciated that the use of the disclosed pneumatic drilling chip removal system will reduce the cost of drilling wells, will decrease drilling time, and will enhance environmental safety.